This invention relates to a focusing technique or apparatus for determining the maximum resolution for projected images.
The prior art is replete with a number of patents which describe automatic focusing equipment for various photographic aids. Many of the systems described in the prior art are quite complex and involve various techniques and methods to implement or aid in obtaining maximum resolution for a photographic enlarger, a projector or a camera. Many such systems employ mechanical techniques, while various other systems use optical methods and techniques. Examples of certain prior art techniques can be found when referring to the following patents:
U.S. Pat. No. 3,249,007 entitled AUTOMATIC FOCUSING PHOTOGRAPHIC PROJECTOR issued on May 3, 1966 to N. L. Stauffer describes an optical sensing arrangement which focuses a pattern of light at the plane of a slide which is to be projected. A reflected portion of the pattern is then focused on a pair of photocells which are responsive to the position of the image. One varies the focusing of the projector until the output from the photocells is equal, which null condition corresponds to a proper focus.
U.S. Pat. No. 3,678,835 entitled AUTOMATIC FOCUSING DEVICE FOR CAMERAS AND THE LIKE issued on July 25, 1972 to Takishima describes an automatic focusing device which employs a chopper positioned in front of a mirror. The chopper directs two different light beams on a common photoelectric element. One obtains two different AC signals which are applied to an amplifier which controls a servo motor operative to focus the camera.
Other patents as U.S. Pat. No. 3,735,686 and U.S. Pat. No. 3,930,261 show automatic focusing schemes which also employ optical aids such as photocells to aid in focusing. The difficulty with such systems is that they are relatively complicated in that they require special components, special types of filters and in general, are fairly difficult to implement and relatively expensive to fabricate.
Focusing which is done in a photographic studio or laboratory is usually dependent upon the visual acuity of the operator and hence, depending upon his skill and familiarity with the mechanics of the particular focusing systems, the selection of resolution is usually determined by the individual and is completely dependent upon his ability. This, of course, presents a problem in that it limits the operation of such devices to skilled personnel.
It is an object of the present invention to determine the point of maximum projected resolution by employing a simple apparatus which serves to provide a signal when maximum projected resolution is obtained. The furnishing of this signal completely obviates the problems associated with normal focusing and hence, enables personnel who are not skilled to perform enlargement or other operations in the photographic laboratory.
While the invention is directed to be used with an enlarger, it has applicability for use in providing maximum resolution for other devices such as cameras, projectors and so on.